Anomalocaris: The weaker apex predator

New findings from biomechanical studies on the arachnid-like front “legs” of Anomalocaris canadensis, an extinct apex predator, challenge previous assumptions about its strength. The marine animal, measuring 2 feet (60 centimeters) in length, was believed to be a formidable creature responsible for crushing the exoskeletons of trilobites. However, a study published in the journal Proceedings of the Royal Society B suggests that Anomalocaris was likely weaker than initially assumed.

Anomalocaris canadensis, discovered in the late 1800s, was known for its peculiar appearance, earning it the name “weird shrimp from Canada” in Latin. It was previously thought to have preyed upon trilobites, leaving behind scarred and crushed exoskeletons in the fossil record. However, the researchers involved in the study question this assumption, considering trilobites’ robust and rock-like exoskeletons compared to Anomalocaris’ soft and pliable body.

The recent research focused on the mouthparts of Anomalocaris, which are armored and ring-shaped, casting doubt on the predator’s ability to consume hard food. To further investigate this matter, the study aimed to explore the capabilities of Anomalocaris’ long, spiny front appendages in processing prey.

Lead author Russell Bicknell, a postdoctoral researcher from the American Museum of Natural History’s Division of Paleontology, conducted the study while affiliated with the University of New England in Australia. Bicknell’s curiosity was piqued by the mismatch between the strength of trilobite exoskeletons and the presumed predatory abilities of Anomalocaris.

The findings suggest that Anomalocaris was likely an agile and fast creature, specializing in capturing soft prey in open water rather than pursuing hard-shelled organisms on the ocean floor. This study sheds new light on the behavior and ecological niche of one of the largest animals to have existed during the Cambrian period.

A close-up on the head of a complete specimen of Anomalocaris canadensis from the Cambrian Burgess Shale of Canada, showing the maximum frontal appendage flexure. Credit: © Alison Daley

An international team of scientists from Germany, China, Switzerland, the United Kingdom, and Australia collaborated on the research. They embarked on the study by constructing a three-dimensional reconstruction of Anomalocaris canadensis using exceptionally well-preserved, albeit flattened, fossils discovered in Canada’s Burgess Shale formation, which dates back 508 million years. To draw parallels, the researchers drew inspiration from modern whip scorpions and whip spiders.

By studying these analogs, the team demonstrated that the segmented appendages of A. canadensis were capable of seizing prey and exhibited both extension and flexion. To assess the mechanics involved, they employed finite element analysis, a modeling technique that revealed stress and strain points in the predator’s grasping behavior. The results indicated that Anomalocaris’ appendages would have suffered damage when attempting to grasp hard-shelled prey like trilobites.

To gain insights into the predator’s swimming behavior, the scientists employed computational fluid dynamics. They subjected the three-dimensional model of Anomalocaris to a virtual current, allowing them to predict the most likely body position it would have assumed while swimming.

This multidisciplinary approach, combining anatomical reconstructions, biomechanical modeling, and computational simulations, has contributed to a better understanding of Anomalocaris canadensis and its predatory capabilities. The research findings challenge previous assumptions and provide new insights into the lifestyle and feeding habits of this remarkable creature from the Cambrian period.

A pair of Anomalocaris canadensis appendages. Credit: © Alison Daley

This groundbreaking scientific paper represents the first instance of combining these biomechanical modeling techniques, providing a fresh perspective on Anomalocaris canadensis compared to previous assumptions. The findings paint a revised picture of this creature, indicating that it was a swift swimmer, actively pursuing soft-bodied prey within the water column while extending its front appendages.

The conventional understanding portrayed these animals as opportunistic feeders, perceiving the Burgess Shale fauna as an abundant food source, consuming whatever they pleased. However, the study’s outcomes challenge this simplistic notion, revealing that the dynamics of the Cambrian food webs were likely far more intricate and complex than previously envisioned.

Lead author Russell Bicknell emphasizes the importance of these new insights, stating that they unveil a deeper understanding of the ecological interactions during the Cambrian period. The research hints at a more sophisticated interplay among the organisms within ancient marine ecosystems, suggesting that Anomalocaris canadensis had a specific role as an agile predator targeting soft prey.

Source: American Museum of Natural History

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